Re: [syzbot] KASAN: use-after-free Write in sco_sock_timeout
From: Desmond Cheong Zhi Xi <hidden>
Date: 2021-08-29 14:53:18
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On 29/8/21 4:29 pm, Hillf Danton wrote:
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On Fri, 27 Aug 2021 15:58:34 +0800 Desmond Cheong Zhi Xi wrote:quoted
On 27/8/21 9:19 am, Hillf Danton wrote:quoted
On Thu, 26 Aug 2021 09:29:24 -0700quoted
syzbot found the following issue on: HEAD commit: e3f30ab28ac8 Merge branch 'pktgen-samples-next' git tree: net-next console output: https://syzkaller.appspot.com/x/log.txt?x=13249c96300000 kernel config: https://syzkaller.appspot.com/x/.config?x=ef482942966bf763 dashboard link: https://syzkaller.appspot.com/bug?extid=2bef95d3ab4daa10155b compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16a29ea9300000 The issue was bisected to: commit e1dee2c1de2b4dd00eb44004a4bda6326ed07b59 Author: Desmond Cheong Zhi Xi [off-list ref] Date: Tue Aug 10 04:14:10 2021 +0000 Bluetooth: fix repeated calls to sco_sock_killTo fix the uaf, grab another hold to sock to make the timeout work safe. #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git e3f30ab28ac8--- a/net/bluetooth/sco.c +++ b/net/bluetooth/sco.c@@ -190,15 +190,14 @@ static void sco_conn_del(struct hci_conn sco_conn_unlock(conn); if (sk) { - sock_hold(sk); lock_sock(sk); sco_sock_clear_timer(sk); sco_chan_del(sk, err); release_sock(sk); - sock_put(sk); /* Ensure no more work items will run before freeing conn. */ cancel_delayed_work_sync(&conn->timeout_work); + sock_put(sk);
Hi Hillf, Saw that this passed the reproducer. But on closer inspection, I think what's happening is that sco_conn_del is never run. So the extra sock_hold prevents a UAF, but that's because now the reference count never goes to 0. In my opinion, something closer to your previous proposal (+ also addressing other calls to __sco_sock_close) where we call cancel_delayed_work_sync after the channel is deleted would address the root cause better. Just my two cents.
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} hcon->sco_data = NULL;@@ -212,6 +211,8 @@ static void __sco_chan_add(struct sco_co sco_pi(sk)->conn = conn; conn->sk = sk; + /* make timeout_work safe; will be put in sco_conn_del() */ + sock_hold(sk); INIT_DELAYED_WORK(&conn->timeout_work, sco_sock_timeout); --